AbbreviationsC CervicalDIP Distal interphalangealFDP Flexor digitorum profundusFDS Flexor digitorum superfi cialisMCP MetacarpophalangealPIP Proximal interphalangealT ThoracicTFCC Triangular fi brocartilagenous complex

IntroductionThe human hand is unique in the animal world in its ability to manipulate the surrounding envi-ronment. The intricate movements of the hand are made possible by precise balance between our joints, ligaments, tendons, and muscles. A

detailed knowledge of anatomy is necessary for our ability to understand the disease processes that affect the hand. Hand injuries account for a signifi cant portion of all emergency room admis-sions.2,10 We injure our hands both at play and at work. Inherited diseases and arthritis often affect the function of the hand as well. The hand exami-nation is even more complicated for children and unconscious patients who cannot cooperate with an orderly hand examination. It is necessary to understand how to diagnose an injury without their specifi c help. As a result of these factors, a detailed understanding of hand anatomy will lead to the best potential outcome and treatment for the disease processes of the hand.

The understanding of the anatomy needs to span the skin surface down into the joints them-selves. Anatomic characteristics specifi c to the hand include a dorsal skin that is thin, pliable, and elastic. It allows for fl exion and extension over a great range, with the superfi cial extensor tendons gliding beneath the subcutaneous tis-sue. On the palmar surface of the hand, the skin is more irregular and completely hairless. It is fi xed to the underlying skeleton through tough septa, which ultimately blend with palmar fascia to provide wearability as well as traction for pinch and grasp. Without this ability, the gliding skin would develop excess roll on attempted grip. It is notable that the difference between the palmar and dorsal aspect of the hand is also manifested in disease states such as edema, which is seen dorsally, but because of the dense underlying connective tissue on the volar side,

34Hand Anatomy and ExaminationSteven L. Bernard and Benjamin Boudreaux

SummaryThe purpose of this chapter is to give a com-prehensive review of hand anatomy and then to further apply that anatomy toward a func-tional examination. With that in mind, this chapter is divided into sections of anatomy, including subsections on arteries, nerves, muscles, nail, and skin as well as bony anat-omy. In each of these sections, fi ne points on the examination of these structures will be included.

M.Z. Siemionow and M. Eisenmann-Klein (eds.), Plastic and Reconstructive Surgery, 469Springer Specialist Surgery Series, © Springer-Verlag London Limited 2010

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the palm will appear relatively innocuous. This could lead to the erroneous conclusion that a disease process is more dorsal than palmar. When viewing this from the aspect of pathology, this also prevents accumulation of pus leading to palmar infections that extend into the dorsal skin.

The Hand Proper

The subtleties of anatomic differentiation within the skin of the hand deserve further clarifi ca-tion. The skin over the thenar eminence is thin-ner than that of the skin over the hypothenar eminence, which in turn is thinner than the skin over the dorsal aspect of the hand and heads of the metacarpal. Superfi cial examination of the hand reveals an immediate differentiation between the dorsal and palmar aspects of the hand. The dorsal skin is essentially a continua-tion of forearm skin, whereas the palm contains glabellar skin with the whirls that ultimately make up our fi ngerprints. The palmar skin is densely invested with connections to the palmar fascia, limiting the mobility of the skin over the underlying bones and allowing us to withstand great pressure during grip and function of the hand. The thickened palmar fascia is called the palmar aponeurosis. This is an extension of the palmaris longus tendon, which forms longi-tudinal bands that extend into the central portion of each fi nger. Pathologically, these can become thickened into chords in Dupuytren’s Contracture. Proximally the aponeurosis blends into the transverse carpal ligament; distally it widens into four slips that blend into the corre-sponding fi brous digital sheaths and lateral liga-ments of the metacarpals incasing the digital nerves and arteries. At their deepest extent, they attach to fi bers that invest in the bones of the hand.

ArteriesThe vascular supply to the arm is based on the axillary artery and its continuation into the lower arm as the brachial artery (Figure 34.1). The brachial artery courses along the medial intramuscular septum between the biceps and triceps muscles and enters the antecubital fossa medial to the bicipital aponeurosis. The major

branches of the brachial artery include the pro-found brachii, superior and inferior ulnar collat-eral, and biceps myocutaneous arteries, as well as direct cutaneous perforators. The artery ends by dividing into the radial and ulnar arteries approximately 1 cm distal to the elbow joint.

The radial artery courses laterally over the tendon of the biceps muscle and over the fascia of the fl exor digitorum superfi cialis (FDS) mus-cles in between the fl exor carpi radialis and bra-chioradialis at the level of the wrist. After coursing under the “anatomic snuffbox,” the radial artery courses beneath the extensor polli-cis longus onto the dorsum of the hand. The dor-sal carpal branches of radial artery unite with a similar contribution from the ulnar artery as well as branches from the interosseous arteries to form the dorsal carpal rete, which supplies the dorsal skin and dorsal metacarpal arteries. The dorsal branch of the radial artery also gives off a large deep branch that travels between the two heads of the fi rst dorsal interosseous muscle and divides into the princeps pollicis and deep pal-mar arch.18

The ulnar artery is the more dominant branch of the brachial artery in most people. After the splitting of the brachial artery, it runs medially beneath the median nerve and the proximal por-tion of the FDS muscle. It continues between the fl exor digitorum profundus (FDP) and the fl exor carpi ulnaris muscle until it reaches the level of the wrist. At the level of the wrist, it is just lateral to the fl exor carpi ulnaris tendon and travels along with the ulnar nerve through Guyon’s canal of the transverse carpal ligament. At the base of the origin of the hypothenar muscles, the vessel divides into a deep and superfi cial arch. Within the proximal forearm, the ulnar artery branches into the recurrent ulnar artery at the level of the FDS origin. Just distal to this the common interosseous artery arises deep to pronator teres and divides into an anterior and posterior branch. The posterior branch goes through the interosseous membrane and sup-plies the dorsal extensor musculature.

Within the hand, the superfi cial palmar arch is the continuation of the ulnar artery and the superfi cial branch of the radial artery. It crosses the palm above the fl exor tendons and just superfi cial to the digital nerves deep to the pal-mar fascia.8,18,27,28 The level of the arch is approxi-mately equal to a line drawn from a fully radially

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abducted thumb. The arch terminates into the palmar digital branches, including the common digital arteries that ultimately divide into the proper digital arteries traveling fi rst volar and ultimately dorsal to the digital nerves. There is a great deal of variability4,20,32 within the vascular system of the hand; however, ultimately consis-tent anatomy of two palmar and smaller dorsal digital arteries can be found in each fi nger and the thumb.3 A deep arch is also formed by a branch of the ulnar artery ultimately connecting with the princeps pollicis from the dorsal branch of the radial artery.

NervesBrachial Plexus

The complex origin of the brachial plexus are cervical nerve roots 5 through 8 (C5–8) and the fi rst thoracic root (T1) with occasional contri-butions from either C4 or T2 (Figure 34.2). Portions of the roots merge to form the upper middle and lower nerve trunks, which travel with the subclavian vessels.16 At the level of the clavicle, the nerves intertwine to form the pos-terior, lateral, and medial cords. These structures

Figure 34.1. Arterial anatomy of the arm.

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intermingle again to divide into the major peri-pheral nerves of the arm. The posterior cord gives rise to the axillary and radial nerves; the lateral cord gives rise to the musculocutaneous and contributes to a portion of the median nerve. The medial cord gives off the remaining fi bers of the median nerve and forms the ulnar nerve as well. As a result of their superfi cial position, the median, ulnar and musculocutane-ous nerves are susceptible to penetrating injury, whereas the axillary and radial nerves are more commonly injured during dislocation of the shoulder. The axillary nerve itself provides motor innervation to the deltoid muscle and sensory innervation to the posterior aspect of the shoulder. The musculocutaneous22 nerve innervates the coracobrachialis, biceps brachia,

and brachialis muscles and supplies sensation to the proximal radial forearm.

Median Nerve

The median nerve is one of three principle motor and sensory nerves of the upper extremity. In its course in the upper arm, it provides no motor or sensory branches. As it enters the forearm between the two heads of the pronator teres, the nerve courses on the deep surface of the FDS muscle and gives off direct motor branches to the pronator teres, fl exor carpi radialis, FDS, and palmaris longus muscles. A major branch of the median nerve in the forearm is the ante-rior interosseous nerve, which runs along the volar surface of the interosseous membrane and

Figure 34.2. Brachial plexus.

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innervates the fl exor digitorum profundus to the index and long fi ngers as well as the fl exor pol-licis longus and the pronator quadratus muscles. At the level of the wrist, the median nerve travels deep to the palmaris longus tendon traversing the carpal tunnel. In the hand, the nerve pro-vides motor innervation to a portion of the opponens pollicis, abductor pollicis brevis, and the fl exor pollicis brevis through its recurrent motor branch to the thenar musculature. From a sensory standpoint, the median nerve gives off branches to the palmar digital nerves of the thumb, index, and the middle and radial palmar digital nerves of the ring fi nger (Figure 34.3).

As the median nerve terminates into the digi-tal nerves, the nerves themselves lie in the pal-mar aspect of the hand. Within the fi nger, the nerve runs with the digital artery and is bor-dered by Cleland’s ligament dorsally and Grayson’s ligament volarly.12 At the level of the distal interphalangeal joint, the digital nerve

terminates into three branches: nail bed, tip, and pulp. Two-point discrimination along the axis of each digital nerve should be less than 6 mm in an adult to suggest an intact nerve.

Ulnar Nerve

As with the median nerve, the main target of the ulnar nerves is the forearm and hand. It courses along the medial aspect of the arm and gives off the medial antebrachiocutaneous nerve at the mid arm level, supplying sensation to the medial arm and forearm. As the ulnar nerve enters the forearm, it travels between the two heads of the fl exor carpi ulnaris muscle and supplies this muscle with innervation. The nerve continues between the plane of the fl exor carpi ulnaris and the fl exor digitorum profundus muscles. The nerve gives off branches to the portion of the fl exor digitorum profundus muscle that supplies the ring and small fi nger tendons. Just proximal to the wrist, a dorsal sensory branch supplies the ulnar dorsal aspect of the hand. The nerve tra-verses the transverse carpal ligament through Guyon’s canal with the ulnar artery. Beyond Guyon’s canal, the nerve divides into a superfi -cial sensory branch, which gives off the palmar digital nerves to the small fi nger and ulnar side of the ring fi nger. The other portion of the ulnar nerve just beyond Guyon’s canal becomes the deep motor branch supplying the hypothenar musculature, all interosseous muscles, the lum-bricals associated with the fl exor digitorum pro-fundus to the ring and small fi ngers, the abductor pollicis, and the deep pad of the fl exor pollicis brevis muscle. The proximal ulnar portion on the palmar aspect of the hand is consistently innervated by the ulnar nerve through either a palmar cutaneous branch or the nerve of Henley, which innervates the ulnar artery before giving off branches to the distal forearm and hypothe-nar eminence (Figure 34.4).

Variability of the Ulnar and Median Nerves

Great variability exists between the ulnar and median nerves from person to person and even within the person from the left to the right upper extremity. Sunderland believes that in only half of the cases the median nerve innervates the fl exor digitorum profundus of the index and Figure 34.3. Median nerve course and distribution.

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middle fi ngers and the ulnar nerve innervates the ring and little fi nger profundus. In the remaining cases, there is overlap such that the median nerve encroaches upon the ulnar nerve’s territory.36 This pattern is reversed in the hand, and the ulnar nerve often extends into the terri-tory of the median nerve. Most commonly affected muscles are the thenar eminence, fi rst or dorsal interosseous, and the lumbricals. In addition to the overlap between the two nerves, there are often interconnections between the nerves. The so-called Martin–Gruber anastomo-ses are interconnections of the median and ulnar nerves in the forearm.

Within the hand, similar connections occur between the median and ulnar nerves, known as Riche–Cannieu7,31 and may be present in as many as 70% of people.

These interconnections are important when examining for specifi c nerve injuries, because the function of muscles normally innervated by either the median or the ulnar nerves can remain

intact, thereby masking complete injuries to the nerves themselves.

Radial Nerve

Originating from the posterior chord of the brachial plexus, the radial nerve begins medial to the triceps and travels posterior through the muscle behind the shaft of the humerus. The nerve then courses anteromedially between the brachialis and brachioradialis muscles over the lateral epicondyle.29 In the upper extremity, the radial nerve innervates the teres major, deltoid, triceps, brachioradialis, anconeus, and extensor carpi radialis longus muscles.

Just distal to the elbow, the nerve divides into two major branches. The superfi cial branch innervates the extensor carpi radialis brevis muscle and provides sensation to the radial aspect of the forearm and dorsal hand. The deep branch of the nerve, the posterior interosseous, runs through the two heads of the supinator muscle beneath the arcade of Frohse and inner-vates the supinator, extensor digitorum commu-nis, extensor carpi radialis brevis, extensor carpi ulnaris, extensor pollicis longus, abductor pollicis longus, extensor pollicis brevis, extensor digiti minimi, and extensor indicis proprius. Sensation to the fi ngers extends approximately to the proximal interphalangeal (PIP) joint level on the dorsal aspect of the hand (Figure 34.5).

Muscles and TendonsThe muscles of the upper arm are separated into two functional compartments by the humerus and medial and lateral intermuscular septi. These compartments are labeled anterior and posterior. The muscles of the anterior compart-ment include the brachialis, and coracobrachia-lis, which fl ex the elbow while the other muscle of the upper arm, the biceps, both fl exes the elbow and supinates the forearm. The sole mus-cle within the posterior compartment is the tri-ceps. Several muscles traverse the elbow joint on their way to infl uencing the fl exion of the elbow, the wrist, and, in some cases, the fi ngers.

Volar Forearm Compartment

The fl exor system of the wrist and hand com-prises muscles that originate in the proximal

Figure 34.4. Ulnar nerve course and distribution.

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two-thirds of the volar compartment of the fore-arm, with tendinous extensions that insert into the wrist or digits (Figure 34.6). There are two fl exor tendons for each fi nger and one for the thumb. The FDS inserts into the proximal to mid-portion of the middle phalanx and creates fl exion at the PIP joint. The fl exor digitorum profundus tendons insert into the distal phalan-ges and fl ex the distal interphalangeal (DIP) joints of each fi nger. The one fl exor of the thumb is the fl exor pollicis longus that inserts into the distal phalanx of the thumb. This causes fl exion of the thumb’s only interphalangeal joint.

The cross-sectional anatomy of the forearm is best viewed in layers (Figure 34.7).9,11,17 The most superfi cial layer contains the palmaris longus, fl exor carpi radialis, fl exor carpi ulnaris, and pronator teres. These muscles either insert into the palmar fascia or the metacarpals and are involved in wrist fl exion or forearm pronation. The second layer of the forearm contains the FDS muscle. The muscle itself originates from two heads and separates into four tendons. The

ring and long fi nger tendons arise from the superfi cial portion of the muscle and therefore traverse the wrist in a superfi cial position. The deeper portion of the FDS muscle belly termi-nates in the FDS tendon of both the index and small fi ngers. As the tendons traverse the hand, they fl atten and split into radial and ulnar slips, which eventually rotate 180° to encompass the fl exor digitorum profundus (FDP) tendons of the individual fi ngers. They then pass dorsally to the profundus tendon and reunite to insert in the proximal half of the middle phalanx of each fi nger. The split of the FDS tendon is called the Chiasm of Camper. The next deeper layer of the forearm consists of the fl exor digitorum profun-dus muscle and the fl exor pollicis longus. Although we have individual control over the FDS to each fi nger, in most instances, the fl exor digitorum profundus muscle is a conjoined mass that acts as one fl exor and lacks individual con-trol to each of the fi ngers. The tendons insert at the base of the distal phalanx on the palmar aspect of the bone itself. It is of note that when looking at the function of the FDS, and the fl exor digitorum profundus tendons6 Baker, Gaul, Williams and Graves have shown that 34% of small fi ngers have an insuffi cient FDS tendon. In addition, it is possible that the FDS tendons to both the ring and small fi nger act in concert. Both of these cases do not allow for isolated fl exion of the PIP joint of the small fi nger. The deepest layer of the volar forearm contains the pronator quadratus muscle, a fl at transverse muscle that assists in pronation of the forearm.

Dorsal Forearm Compartment

Extension of the wrist and fi ngers can be broken down into an extrinsic and intrinsic portion. In the extrinsic system, the muscle bellies origi-nate within the forearm. Within the intrinsic system, the muscles all originate within the hand (Figure 34.8).

The dorsal forearm is divided into a superfi -cial and deep muscle group. The superfi cial group consists of the wrist extensors, including the extensor carpi radialis brevis, the extensor carpi radialis longus, extensor carpi ulnaris, the extensor digitorum communis, and the extensor digiti quinti minimi. These muscles arise from the distal forearm and the lateral epicondyle. This group is often subdivided into the muscles of the “mobile wad,” including the brachioradialis,

Figure 34.5. Radial nerve course and distribution.

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Figure 34.6. Muscles of the volar arm.

Figure 34.7. Cross-sectional anatomy of the volar forearm just proximal to the carpal tunnel.

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Figure 34.8. Muscles of the dorsal arm.

extensor carpi radialis longus, and extensor carpi radialis brevis.

The deep muscle compartment of the dorsal forearm includes the extensor pollicis longus and brevis, the abductor pollicis longus, the extensor indicis proprius, and the supinator muscles. The supinator arises from the humerus, whereas the remaining muscles originate from the proximal radius, ulna, and interosseous membrane. As these muscle bellies become ten-dinous and cross the wrist, the deep fascia forms into a strong, thick, retaining structure called the extensor retinaculum (Figure 34.9). Vertical septa originating from the distal radius and ulna create six fi bro-osseous compart-ments. Numbered from radial to ulnar, the fi rst

extensor compartment23 consists of abductor pollicis longus and extensor pollicis brevis ten-dons; the second compartment, the extensor carpi radialis longus and brevis tendons; the third compartment contains only the extensor pollicis longus, whereas the fourth compart-ment contains the extensor digitorum commu-nis, as well as the extensor indicis proprius tendon; the fi fth compartment contains the extensor digiti quinti minimi tendon; and fi nally the sixth compartment contains the extensor carpi ulnaris tendon. Just distal to the extensor retinaculum on the radial side of the wrist is the “anatomic snuff box,” which is bound by the fi rst and third dorsal compart-ments. Within the substance of the extensor

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retinaculum is Lister’s tubercle, which protrudes from the dorsal aspect of the distal radius and forms a useful anatomic landmark. The exten-sor pollicis longus is found immediately ulnar to the tubercle, which acts as a pulley for the tendon, whereas the contents of the second dor-sal compartment are immediately radial to the tubercle.

Intrinsic System

The intrinsic muscles within the hand are respon-sible for the fi ne coordinated movements of the hand. The muscles themselves are completely contained within the hand distal to the carpus. The thenar eminence has four muscles, including the abductor pollicis brevis, fl exor pollicis brevis, opponens pollicis, and adductor pollicis.

The fl exor pollicis brevis and opponens pollicis are innervated by contributions from both the median and ulnar nerves. The median-innervated muscles all lie radial to the fl exor pollicis longus tendon and include opponens pollicis, abductor pollicis brevis, and the superfi cial head of the fl exor pollicis brevis. The median-innervated muscles serve to position the thumb basal joint. The-ulnar innervated thenar muscles include the adductor pollicis, the fi rst dorsal interosseous, and the deep head of the fl exor pollicis brevis. These muscles contribute to key pinch. The abductor pollicis bre-vis is the only muscle solely innervated by the median nerve. This has clinical signifi cance in that

the abductor pollicis brevis can be individually tested to determine if the recurrent branch of the median nerve, which usually arises just distal to the fl exor retinaculum, is intact. These muscles lie within a compartment separated by a fascial sheath that extends from the radial margin of the palmar aponeurosis. The fi nal muscle of this group, the adductor pollicis, is a fan-shaped mus-cle containing both a transverse and oblique head, with its origin from the third metacarpal and its insertion in the base of the proximal phalanx of the thumb. The abductor itself is innervated by the ulnar nerve and has an action similar to the remaining adductors of the fi ngers.

The hypothenar eminence is completely ulnarly innervated and is made up of the abductor digiti quinti, fl exor digiti quinti, and opponens digiti quinti. As with the thumb, a potential space is formed within the hypothenar eminence, which is shut off from the central space by a vertical extension from the palmar aponeurosis. Incisions for draining an abscess in this area are made at the ulnar side of the fi fth metacarpal to avoid damage to the deep branch of the ulnar nerve that innervates these muscles.

The remaining intrinsic muscles act to fl ex the metacarpals and extend the interphalangeal joints (Figure 34.10). These consist of the lumbrical muscles, which are the only muscles in the body to originate from a tendon. They arise from the radial side of the profundus tendon of each fi nger and insert deep to the transverse metacarpal

Figure 34.9. Cross-sectional anatomy of the dorsal forearm just proximal to the extensor retinaculum.

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ligament joining the radial lateral band of the middle and proximal phalanges.8 As they start volar to the axis of the metacarpophalangeal (MCP) joint and end up dorsal to the proximal and distal interphalangeal joints, they extend the PIP and DIP joints while fl exing the MP joint.37 When the lumbrical contracts, it pulls the distal profundus tendon toward the lateral band, decreasing the strength of the contraction at the DIP joint while allowing for more effective extension of the DIP joint. This allows for a balanced grip.5,33

The remaining muscles, the interossei, can be broken into two groups, the dorsal and volar interossei. Four dorsal interossei act as abductors of the fi ngers. The anatomic axis for all of the interosseous is the third metacarpal. The small fi nger is abducted by the abductor digiti quinti previously mentioned and acts similar to the remaining dorsal interossei muscles. The volar interossei are the adductors, with the middle fi nger acting as the axis again. As such, the middle fi nger has two dorsal interossei and no volar interosseous. Each of the dorsal interosseous mus-cles has two heads, with the exception of the third interosseous. The superfi cial head of the dorsal interosseous muscles terminates in a medial

tendon deep onto the lateral tubercle of the base of the proximal phalanx. The deep head of each dor-sal interosseous forms a lateral tendon, which ulti-mately coalesces with the lateral band of the extensor hood of the fi ngers. This tendon starts palmar to the MCP joint axis and, like the lumbri-cals, ends up dorsal to the PIP and DIP joints. As with the lumbricals, the interossei fl ex the MCP joints and extend the PIP and DIP joints.

More distally the oblique fi bers or spiral fi bers of the lateral bands sweep over the proximal inter-phalangeal joint joining the central tendon, ulti-mately terminating in the conjoined lateral bands that unite at the level of the distal third of the middle phalanx to form the terminal tendon inserting on the base of the distal phalanx to extend it.24

Unlike the dorsal interossei, the volar interos-sei have only one muscle head and insert into the ulnar lateral band of the index fi nger and the radial lateral band of the ring and small fi ngers. As such, these tendons do not attach onto the proximal phalanx itself. All of the interosseous muscles and the lumbricals to the ring and small fi ngers are innervated by the ulnar nerve, whereas the lumbricals to the index and middle fi ngers are innervated by the median nerve.

Figure 34.10. Extensor mechanism of the index, including the lumbrical muscle, fi rst dorsal interosseous muscle, and extensor hood. Flexor vincula blood supply represented as well.

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Figure 34.11. Bones of the wrist. Spiral line represents the order of calcifi cation of each bone.

Bony and Ligamentous AnatomyWrist

An understanding of the anatomy of the normal wrist is required before appreciating functional loss from diseases of the wrist. The distal ulna articulates with the radius in the sigmoid notch. This is known as the distal radioulnar joint, and movement through that joint is pronation and supination of the hand. In the normal wrist, the distal portion of the ulna is shorter than the ulnar portion of the distal radius. This allows room for the articular disc known as the triangular fi bro-cartilagenous complex (TFCC).1 The TFCC is a fan-shaped structure that acts as a hammock-like sling to the ulnar side of the wrist.

This distal radial ulnar joint supports the eight carpal bones (Figure 34.11). The proximal row includes the scaphoid, lunate, triquetrum, and pisiform bones. The pisiform bone is a load-bearing sesamoid bone of the wrist and is formed within the substance of the fl exor carpi ulnaris tendon. Is has a function that is similar to that of the patella and is essentially separate from the remaining bones of the wrist. The distal row is formed by the trapezium trapezoid capitate and hamate. It is of note that the scaphoid itself extends

into the distal row as well. The carpal bones have both intrinsic and extrinsic ligaments. The intrinsic ligaments are confi ned within the carpal bone themselves, whereas the extrinsic ligaments extend from the carpus to the radius and ulna proximally and metacarpals distally. Important ligaments of the extrinsic system include the radial collateral ligament as well as the radioscaphocapitate, radiolunate, and radioscapholunate ligaments. On the ulnar side of the wrist, the important extrinsic ligaments include the ulnar collateral ligament as well as the meniscus, palmar ulnocarpal ligament, and the TFCC itself. The space of Poirier is present due to the absence of a volar lunocapitate ligament. With the exception of this, the palmar ligaments are markedly stronger than the dorsal ligaments. The overall arrangement of the eight bones and ligaments that form the carpus is extremely complex. Motion takes place within the radio-carpal joint and the mid carpal joint, each contributing approximately 50% of the overall motion of the wrist. More distally, the index and long fi nger metacarpals are fi rmly attached to the distal row of the carpus and form a fi xed unit of the hand. The metacarpals of the ring fi nger and particularly the small fi nger have increased motion that allows for cupping of the palm.

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From a pathologic standpoint, it is most helpful to consider the proximal row as one unit that acts as a strong spring in tension. On the thumb side, the scaphoid bone tips palmar to the plane of the wrist, and the tendons pulling of the thumb cause it to act as a cantilever, whose force is held in check by dorsal tension on the trique-tral bone. As the lunate is central to both the scaphoid and triquetral bones, it becomes key to understanding pathology of the wrist.15 When the radial side of the wrist has a disruption either through a fracture of the scaphoid or tear in the scapholunate ligament, the spring is bro-ken, and the scaphoid itself tips down, which in turn releases tension, causing the lunate and the still attached triquetrum to tip dorsally. Likewise, a disruption between the lunate and the tri-quetrum will cause the lunate, still attached to the scaphoid, to tip palmarly. A more detailed

description of this can be obtained in the section on wrist instability. Just distal to the carpal bones are the fi ve metacarpals. Motion between the carpus and metacarpals is limited in the fi n-gers, but within the thumb, the carpal metacar-pal joint is a saddle-type joint and allows for much of the complex motion of the thumb, including abduction, adduction, rotation, and opposition.

Bones of the Hand

The hand consists of fi ve metacarpals and 14 phalanges (Figure. 34.12). Between the metacar-pals and the phalanges are the MCP joints (Figure. 34.13). The MCP joints are all similar in that they act like a hinge. Because the head of the metacarpal is oblong, as the MCP goes through fl exion, the proximal phalanx moves away from

Figure 34.12. Bones of the hand.

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Figure 34.13. Joints of the hand.

the axis of rotation therefore tightening the col-lateral ligaments. The collateral ligaments of the MCP joint are broken into a proper and acces-sory ligament.21 The proper collateral ligaments allow for stability with the MCP joint in exten-sion, whereas the accessory ligaments become progressively tighter as the MCP joint is fl exed, and the fl are of the head and eccentric axis elon-gates these fi bers, causing greater stability with greater fl exion. Deep structures are the joint capsule itself, which is a loose areolar tissue lat-erally and dorsally and coalesces into the thick volar plate supporting the base of the fl exor ten-don sheath.

The volar plate of the MCP joint lacks check ligaments as opposed to the PIP and DIP joints that both contain check ligaments lining the lateral aspect of the phalanges proximal to the volar plate. The flexor digito-rum profundus and superficialis tendons are contained volarly within the tendon sheaths. These form a retaining system that prevent bow stringing of the flexor tendons as the fin-

ger is flexed. Transverse thickenings of the tendon sheaths are called annular pulleys (Figure 34.14). The first pulley (A1)38 is asso-ciated with the volar plate and MCP joint and is deep to the distal palmar crease; the second pulley originates from the proximal phalanx; the third pulley is associated with the volar plate of the PIP joint; the fourth pul-ley, the middle phalanx, whereas the fifth pul-ley is just at the level of the volar plate of the DIP joint.13 Between the annular pulleys are cruciate pulleys C0–C3. These pulleys are made of looser tissue in a cross arrangement, allowing for flexion at near the joints, whereas the stiffer annular pulleys still retain the tendons close to the axis of each joint. Functionally, these pulleys improve the effi-ciency of flexion through decreased tendon excursion.25,26 The trade-off is less power than if the pulleys were absent.

The anatomy of the pulley system in the thumb differs from that of the fi ngers in that there are two annular pulleys located over the

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volar plates of the MCP and IP joint, whereas the pulley over the proximal phalanx is oriented in an oblique fashion and is named the oblique pulley.14 It is an extension of the adductor pollicis aponeurosis and is the main restraint preventing bowstringing of the fl exor pollicis longus tendon.

Within the fl exor tendon sheath, the tendons obtain a blood supply from the vincula, which are vessels carrying structures that originate on the volar aspect of the bone and insert on the dorsal aspect of each tendon (Figure. 34.10). Each of the FDS tendon and FDP tendon has one short and one long vincula. The vincula brevia is located at the fl exor tendon’s insertion, whereas the vincula longa is located more prox-imally. These vascular leashes will often arrest proximal movement of the fl exor tendons in trauma cases wherein the tendons have been transected.34

Epiphyseal Anatomy

When considering the anatomy of the hand, it is also important to understand the difference between the bony anatomy of children and that of adults. The most obvious difference is noted on radiographs of the epiphysis. When inter-preting a radiograph, it is important to note that newborns lack enough calcium to demonstrate a distinct epiphysis or even a bone if young enough. Within the hand, the epiphyses become demonstrable at varying times from approxi-mately 10 months to 3 years, depending on the child and the specifi c bone (see spiral in Figure. 34.11).19,35 All epiphyses of the fi ngers and meta-carpals are closed by approximately 14–16 years of age, whereas the epiphyses of the radius and ulna close between 16 and 18 years of age. Boys generally lag behind girls. Within the metacar-pals and phalanges, the epiphyses of the

Figure 34.14. Flexor pulley system.

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metacarpals are seen distally, whereas in the phalanges they are all proximal. The exception to this is the epiphysis of the metacarpal of the thumb, where it is proximal and is similar in appearance to the three phalanges of the fi ngers (Figure 34.15).

Finger Tip and FingernailThe anatomy of the fi ngertip warrants a separate discussion. The fi ngertip is defi ned as every-thing distal to the insertion of the extensor and fl exor tendons of the distal phalanx. Tissues include the skin, nail, subcutaneous fat, and

bone (Figure 34.16).39 The pad of the volar skin is attached to the underlying distal phalanx by vertically oriented tough fi brous septa.

The fi ngernail is important for stabilization, sensation, and cosmetic appearance. The nail and surrounding skin are called the periony-chia. More specifi cally, the skin folds along the side of the nail are called the paronychia, while the junction between the nail fold proximal to the nail is the eponychium. The hyponychia is the junction of the distal part of the nail and the skin of the fi nger at the point that the nail leaves the nail bed.

The nail grows approximately 0.1 mm per day. At this rate, it takes approximately 3 months to

Figure 34.15. Epiphyseal anatomy of the hand.

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Figure 34.16. Fingertip anatomy.

grow from the eponychium to the fi ngertip. In addition to this time, there is an approximately 3-week delay before a nail begins to grow after injury. This delay is followed by an increase in nail formation over the next 50 days, causing a bulge. It takes approximately three full nail growths before the nail reaches a fi nal appearance after injury. The dorsal roof and ventral fl oor of the eponychial fold along with the nail bed all contribute to the growth of the nail. The ventral fl oor from the proximal end of the nail fold just distal to the insertion of the extensor tendon out to the end of the lunula provides approximately 90% of the growth. The lunula is the moon-shaped whitish opacity at the proximal end of the nail, resulting from nail cell nuclei within the germinal matrix of the nail itself.

Blood supply to the nail is from terminal branches of the volar digital artery. Blood vessels and nerves of the nail coalesce distally to form the glomus, which is a thermal regula-tory organ that contributes to the modulation of peripheral circulation. The tip of the distal phalanx reaches to approximately the mid portion of the fingernail bed. The end of the distal phalanx is composed of hard cortical bone and is referred to as the distal tuft. Although this density contributes to the strength of the distal phalanx, it also increases the amount of time required for healing of fractures in the distal phalanx.

ConclusionIn conclusion, before treating diseases of the hand, a deep understanding of the anatomy and physiology is important. Review of this chapter should serve as a basis for further specialized study within each separate anatomic area.

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